Surgery on the human eye has become commonplace in recent years. Many patients pursue eye surgery as an elective procedure, such as to avoid the use of contacts or glasses, and other patients may find it necessary to pursue surgery to correct an adverse condition in the eye. Such adverse conditions may include, for example, cataracts or presbyopia, as well as other conditions known to those skilled in the art that may negatively affect elements of the eye. For example, a cataract may increase the opacity of the lens of the eye, causing impaired vision or blindness. Correction of such adverse conditions may be achieved by surgically removing a diseased lens in the patient's eye and replacing it with an artificial lens, known as an intraocular lens (IOL).
The anatomy and physiology of the human eye is well understood. Generally speaking, the structure of the human eye includes an outer layer formed of two parts, namely the cornea and the sclera. The middle layer of the eye includes the iris, the choroid, and the ciliary body. The inner layer of the eye includes the retina. The eye also includes, physically associated with the middle layer, a crystalline lens that is contained within an elastic capsule, referred to herein as the lens capsule, or capsular bag.
Image formation in the eye occurs by entry of image-forming light to the eye through the cornea, and refraction by the cornea and the crystalline lens to focus the image-forming light on the retina. The retina provides the light sensitive tissue of the eye.
Functionally, the cornea has a greater, and generally constant, optical power in comparison to the crystalline lens. The power of the crystalline lens, while smaller than that of the cornea, may be changed when the eye needs to focus at different distances.
The iris operates to change the aperture size of the eye. More specifically, the diameter of the incoming light beam is controlled by the iris, which forms the aperture stop of the eye, and the ciliary muscles may contract, as referenced above, to provide accommodation in conjunction with any needed change in the size of the aperture provided by the iris. The opening, or aperture, in the iris is called the pupil.
Correction of defects or degradation in the aspects of the eye may occur surgically, as mentioned above, or non-surgically. In a simple example, it is common to wear glasses or contact lenses to improve vision by correcting myopic (near-sighted), hyperopic (far-sighted) and astigmatic eyesight. Rather than relying on glasses or contacts, elective laser refractive surgery, or other eye surgery, may serve to improve the refractive state of the eye, and may thereby decrease or eliminate dependence on glasses or contact lenses. Additional surgeries may include various methods of surgical remodeling of the cornea, or cataract surgery, for example. Surgery may also serve to implant an IOL, either in addition to the crystalline lens, which addition is referred to as a phakic IOL, or upon removal of the crystalline lens, which replacement is referred to as a pseudophakic IOL.
An IOL may be implanted in the eye, for example, as a replacement for the natural crystalline lens after cataract surgery, or to alter the optical properties of an eye in which the natural lens remains. As such, IOLs may be suitable for correcting vision disorders.
Owing to its thinner shape and the material from which it is made, the absorption of light in an IOL in much of the visible spectrum is negligible. Consequently, the IOL transmits a higher percentage of light than is transmitted by the natural crystalline lens. Thus, the perceived light intensity and/or the contrasting light intensity of objects viewed by an IOL patient may appear unusually bright. This extreme brightness may manifest itself to IOL patients in the form of an increased sensitivity to light. This increased sensitivity may simply annoy the IOL patient, or, of greater concern, may provide a deleterious effect to the IOL patient's ability to perform routine activities requiring acute vision.
A need therefore exists to reduce the light intensity induced by implanted IOLs in IOL patients.